Linepipe Steel With Enhanced Sulfide Stress Cracking Resistance

ABSTRACT

The present disclosure relates to methods and treatments of linepipe steels that transport one or both of crude oil and natural gas. More particularly, the present disclosure relates to sulfide stress cracking resistance of carbon steels for use as linepipe in transporting crude oil and natural gas by alternative thermo-mechanically controlled and/or one or more additional heat treatment processes.

FIELD OF THE INVENTION

This application relates to methods and treatments of linepipe steels that transport crude oil and natural gas.

BACKGROUND OF THE INVENTION

This application relates to linepipe steels that transport crude oil and/or natural gas and, more particularly, to methods and treatments of linepipe steels for enhanced sulfide stress cracking resistance.

High-strength metallic materials, such as high-strength steels, are commonly used, cost-effective materials for forming linepipe for transporting crude oil and natural gas mined from oil or gas fields. These high-strength, cost-effective materials may be selected to permit transportation of large volumes of crude oil or natural gas without compromising the integrity of the linepipe. That is, the high-strength nature of the materials may permit transportation at relatively higher pressures, or the use of relatively thinner linepipe having relatively larger diameters to increase flow volume, and the like. As such, significant cost reduction may be realized from use of such high-strength materials in terms of, for example, material and construction costs.

However, crude oil and natural gas may comprise, among other components, hydrogen sulfide (H₂S) (which may be in relatively high or low concentrations, e.g., extreme to mild sour conditions), as well as other components, such as water, carbon dioxide, chloride, and the like. The presence of H₂S can detrimentally interfere with the operability of a steel linepipe due to sulfide stress cracking (SSC). SSC is a form of hydrogen embrittlement induced by atomic hydrogen that is produced by sour corrosion due to the presence of H₂S on a metal's (e.g., steel's) surface. The products of the sour corrosion include atomic hydrogen, which may be absorbed by the linepipe material, resulting in subsequent SSC. Moreover, the H₂S in crude oil and natural gas can further act as an SSC catalyst because the sulfur in the H₂S prevents recombination of atomic hydrogen into H₂, thereby maintaining a higher concentration of atomic hydrogen available for absorption by the linepipe and, thus, formation of SSC.

SSC susceptibility of carbon steel linepipe may be dependent on a number of factors such as, for example, the microstructure of the compositional metal, inclusion and precipitate distribution, chemical composition, and the like, and combinations thereof. High-strength metallic materials, such as high-strength carbon steels and/or weldments, having heat affected zones with high hardness (e.g., a hardness greater than 248 Vickers hardness number) commonly used to form linepipe may be particularly susceptible to SSC.

SSC can cause linepipe carbon steels to lose ductility (e.g., elongation to rupture) and increase cracking susceptibility, thereby causing the linepipe to fail at stresses below its nominal yield strength when subjected to the mechanical stresses of transporting crude oil and/or natural gas (e.g., tensile stresses, residual or applied, and the like). Structural failure of formed parts can result in severely hazardous environmental and operational conditions, as well as substantial economic losses. Accordingly, metallic materials for use as linepipe for transporting crude oil and natural gas comprising H₂S require high resistance to sour corrosion and/or high resistance to SSC per industry standard requirements.

SUMMARY OF THE INVENTION

This application relates to structural carbon steels that are used to form linepipe that transport crude oil and/or natural gas and, more particularly, to methods and treatments of linepipe carbon steels for enhanced sulfide stress cracking resistance.

In one or more aspects, the present disclosure provides a method including heating a carbon steel composition to a first reheating temperature, the first reheating temperature being greater than about 1175° C., and deforming the composition while the composition is at a temperature in the range of the reheating temperature and a finishing temperature of greater than about Ar3. Thereafter, quenching the composition into a carbon steel plate.

In one or more aspects, the present disclosure provides a carbon steel plate, the carbon steel plate formed according to a method of heating a carbon steel composition to a first reheating temperature, the first reheating temperature being greater than about 1175° C., and deforming the composition while the composition is at a temperature in the range of the reheating temperature and a finishing temperature of greater than about Ar3. Thereafter, quenching the composition into the carbon steel plate.

In one or more aspects of the present disclosure, a method is provided including treating a formed carbon steel; and thereafter, reheating the formed carbon steel to a reheating temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

The following figures are included to illustrate certain aspects of the disclosure, and should not be viewed as exclusive configurations. The subject matter disclosed is capable of considerable modifications, alterations, combinations, and equivalents in form and function, as will occur to those skilled in the art and having the benefit of this disclosure.

FIG. 1 illustrates comparative TMCP methods demonstrating the differences between a traditional low temperature TMCP (tTMCP) methodology and the higher temperature TMCP (htTMCP) methodology of the present disclosure.

FIGS. 2A-2D show representative reconstructed austenite structures at Finishing Rolling Temperature (FRT) and resultant micrographs of steel formed according to the ltTMCP and the htTMCP of FIG. 1 .

FIGS. 3A-3F show representative steel microstructures at Finishing Rolling Temperature (FRT) and resultant micrographs of steel formed according to the htTMCP of FIG. 1 .

DETAILED DESCRIPTION OF THE INVENTION

This application relates to linepipe steels that transport crude oil and/or natural gas and, more particularly, to methods and treatments of linepipe steels for enhanced sulfide stress cracking resistance.

As used herein, the term “linepipe,” and grammatical variants thereof, refers to any tubular linepipe steel that transports crude oil and/or natural gas (or other liquids and/or gases), including pipelines, flowlines, risers, any other transport conduit, and the like, without limitation. When one or more aspects of the present disclosure is described with reference to “pipeline,” for example, the disclosure is equally applicable to any other type of linepipe, without limitation, unless specified otherwise.

The present disclosure advantageously enhances the sulfide stress cracking (SSC) resistance of carbon steels for use as linepipe in transporting crude oil and natural gas by one or more alternative thermo-mechanically controlled processes and/or one or both of two post-steel plate or pipe production heat treatment processes (termed either (1) “interim austenitization treatment processes” or (2) “final heat treatment processes,” as discussed hereinbelow, and grammatical variants thereof).

Carbon steels for use in linepipe are traditionally formed using a thermo-mechanically controlled process (TMCP) under specific conditions. TMCP is a metallic rolling technique in which the mechanical properties of the metal are controlled using a hot deformation process in a rolling mill and transformed during a controlled accelerated cooling process. TMCP is a hot deformation process, and such terminology may be used interchangeably in the industry. Traditional TMCP utilizes relatively low reheating temperature (RHT) (e.g., less than or equal to 1150° C.) and/or relatively low finishing rolling temperature (FRT) (e.g., less than or equal to 900° C.), including one or more deformation steps at these relatively low temperatures, such as hot rolling, along with relatively short interpass times (i.e., time between two consecutive deformation steps) to minimize austenite grain growth. These lower RHT/FRT temperatures are traditionally known to enhance the mechanical properties of the metal by promoting the formation of fine grain sized microstructure transformed from finer prior austenite grains. As a tradeoff for achieving desired mechanical properties, heavy, and costly, rolling equipment is generally required to achieve deformation of the metal at these low temperatures.

Different than traditional methods, the present disclosure provides alternative TMCP manufacturing methodologies that advantageously enhance the SSC resistance of the produced linepipe without compromising other desired mechanical properties. The TMCP methodologies of the present disclosure may be used alone or in combination with the additional subsequent heat treating methodologies.

The present disclosure provides a TMCP process that employs relatively higher RHT and/or higher FRT temperatures compared to traditional TMCP, including one or more deformation (e.g., hot rolling) steps at relatively higher temperatures. It is to be appreciated that small variations in RHT and FRT can have significant effect on microstructure, strength, and SSC resistance of a carbon steel. For these reasons, traditional low temperature RHT (≤1150° C.) and low temperature FRT (≤900° C.) have been used to minimize austenite grain growth. The present disclosure establishes that higher RHT and higher FRT, even if by several degrees, can advantageously alter the microstructure of the resultant steel and its SSC resistance, as described hereinbelow.

Additionally, in some instances, the TMCP described herein further employs one or more relatively longer extended interpass times, as well, to promote recovery and or recrystallization of deformed austenite; extended interpass time parameters are described hereinbelow and, unlike traditional interpass practice, the extended interpass times described herein are controlled such that the interpass time is managed and not otherwise random. After reaching FRT, the TMCP methods include quenching or cooling at a cooling rate. Quenching includes accelerated cooling, wherein a fluid is used to increase cooling rate (as opposed to air cooling); other quenching methods may also be employed, without departing from the scope of the present disclosure. Accelerated cooling may enhance various performance properties of the TMCP-produced steel, such as enhanced low temperature toughness and high fracture toughness. After quenching, a formed carbon steel is produced.

As used herein, the term “formed carbon steel” or “formed steel,” and grammatical variants thereof, refers to a carbon steel composition that has been formed into the shape of a plate (also referred to as a sheet) or seamless pipe and quenched (e.g., cooling by any means, such as to room temperature or other appropriate temperature), such as by the TMCP methods described herein. The formed steel is suitable for use as linepipe for use as pipeline, as described herein, and meet required industry standards (e.g., API 5L, EN ISO 3183, CSA Z245.1, and the like).

The methods of the present disclosure result in coarser (or relatively coarser compared to traditional processes) austenite grain sizes that promote the formation of lath (i.e., long and slender) bainite. The coarser austenite grain sizes enhance the hardenability of the formed steel and favor the formation of lath bainite over the formation of traditional, acicular ferrite and/or granular bainite. The resultant metal, and linepipe manufactured therefrom, benefits from the strong mechanical properties of the lath bainite (e.g., tensile properties, such as low temperature toughness, and the like) while exhibiting enhanced SSC resistance. It is to be understood, however, that although the methods of the present disclosure promote lath bainite, other microstructures, such as acicular ferrite and/or granular bainite, may also be present in the produced metal, without departing from the scope of the present disclosure.

Various aspects of the present disclosure are described hereinbelow by providing comparative description and examples to traditional methodology. It is to be understood that the term “TMCP” will refer to the methodologies of the present disclosure and all “traditional” TMCP references will be labeled as such or similarly. Further, although various specific carbon steel compositions are described herein, it is to be appreciated that the TMCP methodologies of the present disclosure for enhancing SSC resistance are applicable to any and all steel compositions for use in manufacturing linepipe and meeting required industry standards (e.g., API 5L, EN ISO 3183, CSA Z245.1, and the like), without limitation.

Referring first to FIG. 1 , illustrated are comparative TMCP methods graphically demonstrating the differences between a traditional low temperature TMCP (tTMCP) methodology and the higher temperature TMCP (htTMCP) methodology of the present disclosure. Representative, and non-limiting, deformation (e.g., hot rolling) steps are shown as starbursts, further illustrating extended non-limiting interpass times as part of the htTMCP methods of the present disclosure.

As comparatively shown, the traditional ltTMCP demonstrates lower slab reheating temperature (ltRHT) in order to minimize austenite grain growth (keeping the grain size small), and also demonstrates relatively lower finishing rolling temperature (ltFRT) in order to maximize hot deformation below the non-recrystallization temperature (Tnr) and achieve a pancaked or fine grain austenite structure. The ltTMCP produces a primarily fine grained microstructure composed of acicular ferrite, granular bainite or ferrite, or combinations thereof.

With continued reference to FIG. 1 , as comparatively shown, the htTMCP of the present disclosure demonstrates a higher slab reheating temperature (htRHT) to optimize austenite grain growth (encouraging large(r) austenite grain size), and also demonstrates a relatively higher finishing rolling temperature (htFRT) in order to minimize hot deformation below the Tnr and prevent pancaking or deformation of the formed grain structures. The extended interpass time shown (one, non-limiting example shown) in the htTMCP plot of FIG. 1 may promote austenite recovery and recrystallization at the higher temperatures used (e.g., greater than about 1000° C.).

FIGS. 2A-2D show representative reconstructed austenite structures at FRT and resultant micrographs of formed steel according to the ltTMCP and the htTMCP of FIG. 1 . FIG. 2A and FIG. 2B show reconstructed austenite structure at ltFRT and htFRT, respectively of FIG. 1 . The reconstruction of austenite structure was completed through the use of typical orientation relationships between parent austenite phase and daughter bainitic phases based on Electron Back Scattered Diffraction (EBSD) techniques. As shown in FIG. 2B, the austenite structure according to the htTMCP of the present disclosure produces comparatively larger austenite grain structures. Indeed, the average prior austenite grain size (PAG) according to the traditional ltTMCP method was measured at 13.7 μm (FIG. 2A), whereas the average PAG according to the htTMCP method of the present disclosure was measured at 24.9 μm (FIG. 2B). Generally, the average PAG according to the htTMCP methods of the present disclosure are in the range of about 20 μm to about 50 μm, encompassing any value and subset therebetween, such as about 30 μm, or about 40 μm. FIGS. 2C and 2D show micrographs of the resultant formed steel after accelerated cooling according to the ltTMCP and the htTMCP, respectively, of FIG. 1 . As shown, the coarser austenite structure of the htTMCP method of the present disclosure promoted a lath bainite microstructure, as shown in FIG. 2D, which is absent or less apparent in the traditional ltTMCP microstructure shown in FIG. 2C comprising primarily fine(r) grained ferritic and granular bainitic microstructures.

In various aspects of the present disclosure, the RHT may be in the range of greater than or equal to about 1175° C. to about 1350° C., encompassing any subset and value therebetween, such as in the range of about 1200° C. to about 1300° C., more preferably between 1200° C. to 1250° C. The heating rate is not considered to be particularly limiting to reach the desired RHT; in some aspects, the heating rate to RHT may be in the range of about 0.1° C. per second (° C./sec) to about 100° C./sec, encompassing any value and subset therebetween. In one or more aspects, the RHT may be maintained stable for a predetermined length of time (e.g., depending on the steel composition and part size to be produced therefrom, depending on the RHT, and the like, and any combination thereof), such as greater than about one (1) minute to about ten (10) hours, encompassing any values and subset therebetween, such as greater than about 1 hour to about 5 hours. The time period in which the RHT is maintained is also referred to in the industry as the period of “austenitizing.” Accordingly, the austenitizing period described in the present disclosure is performed at a relatively higher temperature compared to traditional TMCP.

In various aspects of the TMCP methods described herein, the FRT may be in the range of the RHT to greater than about Ar3, encompassing any subset and value therebetween, such as about 910° C. to about 1000° C., encompassing any value and subset therebetween. At least one or more extended interpass durations may be in the range of about 10 seconds to about 10 minutes, such as about 30 seconds to about 10 minutes, encompassing any value and subset therebetween. The at least one or more extended interpass durations are performed at or above a temperature in the range of about Tnr (the non-recrystallization temperature) to about (Tnr+200° C.) (i.e., the Tnr temperature plus 200° C.), such as in the range of about Tnr to about Tnr+100° C.), or in the range of about Tnr to about Tnr+50° C.), encompassing any value and subset therebetween. For example, in various aspects, at least one or more extended interpass durations are performed at or above a temperature of about 950° C., encompassing any subset and value therebetween, such as about 30 seconds to about 10 minutes. In various aspects, one or more of the extended interpass durations may be in the temperature range of at least about 950° C. to about 1175° C., encompassing any value and subset therebetween.

Finally, the accelerated cooling (also referred to as quenching) for use in various aspects of the TMCP methods of the present disclosure may be in the range of about 1° C./sec to about 300° C./sec, encompassing any value and subset therebetween, such as about 5° C./sec to about 100° C./sec. The accelerated cooling may be to a temperature of equal to or less than about 500° C., such as in the range of about 100° C. to about 400° C., or about 20° C. (room temperature) to about 400° C., encompassing any value and subset therebetween.

In one or more aspects, the present disclosure incorporates a final heat treatment step after completion of a high temperature TMCP process (i.e., after cooling, and whether the cooled steel is formed or otherwise welded into a pipe). The high temperature TMCP and the final heat treatment step synergistically further enhance SSC resistance without compromising desired mechanical properties (e.g., tensile properties, low temperature toughness/resistance, hydrogen induced cracking, and the like) and with minimal manufacturing costs. It is to be understood that while the final heat treatment process of the present disclosure is described with reference to high temperature TMCP steel formation processes, it is equally applicable to any carbon steel formed by other methodologies, such as traditional TMCP, Electric Resistance Welded (ERW) Pipe, Spiral Welded Pipe, Seamless Pipe, and the like, and any combination thereof.

In one or more aspects, steel formed after completion of a high temperature TMCP process (or other formed steel process) may be subsequently heated (after accelerated cooling to a desired temperature) to a temperature in the range of about (Acl−300° C.) (i.e., the Acl temperature less 300° C.) to about Acl, such as in the range of about (Acl−200° C.) to about Acl, or in the range of about (Acl−100° C.) to about Acl, and preferably in the range of about (Acl−300° C.) to less than Acl, encompassing any value and subset therebetween. Acl is the lowest temperature at which austenite begins to form during heating at a specified rate and, accordingly, is not a static temperature. In one or more aspects, the heating rate may be in the range of about per second (° C./sec) to about 100° C./sec, encompassing any value and subset therebetween; such rates may depend on a number of factors including, but not limited to, the type of heating used (e.g., induction heating v. non-induction heating). In various aspects, the heating temperature for the final heating step after high temperature TMCP may be preferably relatively close to but less than the Acl temperature to maximize SSC resistance. Heat treatment above Acl may potentially cause the formation of hard phase from reverted austenite during cooling, which may deteriorate SSC resistance.

Upon reaching the desired temperature, it is maintained stable for a predetermined length of time, such as in the range of greater than about one (1) minute to about 10 hours, encompassing any value and subset therebetween, such as about 10 minutes to about 8 hours, or about 10 minutes to about 6 hours, or about 10 minutes to about 5 hours, or preferably about 10 minutes to about 3 hours, or about 10 minutes to about 2 hours, and thereafter allowed to cool. The cooling temperature and cooling rate is non-limiting and, therefore, does not constrain the process to any particular cooling equipment or staffing requirement, thereby limiting costs. The cooling may be performed to reach ambient temperature by any suitable means, including air cooling or other passive cooling techniques, in some aspects. In various aspects, cooled high temperature TMCP steel has not been formed into a pipe (e.g., welded) prior to performing the final heat treatment process, after allowing further cooling from the final heat treatment, it may thereafter be formed into a tubular linepipe (e.g., welded).

The TMCP process described herein may be applied to steel compositions manufactured into linepipe by tubular welding techniques, alone or in combination with the final heat treatment process of the present disclosure. In various other aspects, the present disclosure is equally applicable to steel compositions manufactured into linepipe by tubular seamless techniques (“seamless formed steel”), requiring the combination of both the TMCP process (e.g., hot deformation process) and the final heat treatment processes described herein. As used herein, the term “seamless formed carbon steel” or “seamless formed steel,” and grammatical variants thereof, refers to a formed steel, as described hereinabove. Seamless formed steel is shaped during the TMCP processes into a tubular pipe having a hollow section and no seams (as opposed to welded pipe comprising seam welds) and quenched. When the present disclosure provides for a seamless formed steel, the final heat treatment process is mandatory and not optional.

Seamless formed steel is manufactured using TMCP by reheating a steel billet at a RHT. While hot, the steel billet is pierced through the center (e.g., with a rotary piercer and a set of roller arrangements to maintain the piercer at the center of the billet). The billet is rolled and stretched until it meets a desired length, diameter, and wall thickness. For example, the inner diameter of the seamless formed steel may be approximately equivalent to the outer diameter of the rotary piercer, and the outer diameter of the seamless formed steel may be controlled using an external roller arrangement. By controlling the inner and outer diameter of the seamless formed steel, the wall thickness is also controlled.

As with welded formed steel, traditional seamless formed steel is manufactured using traditional TMCP utilizing relatively low RHT (e.g., equal to or less than or equal to 1150° C.) to reheat the billet and austenitize and relatively low FRT (e.g., less than or equal to 900° C.) to roll and stretch the billet, including one or more hot deformation steps at these relatively low temperatures, along with relatively short interpass times (i.e., time between two consecutive deformation steps) to minimize austenite grain growth, and provide fine ferrite/bainite microstructure, as described hereinabove.

Differently, the present disclosure provides for manufacturing seamless formed steel utilizing the high temperature TMCP process to provide coarser (or relatively coarser compared to traditional TMCP processes for forming seamless formed steel) austenite grain size that promote the formation of lath bainite, as described hereinabove.

The present disclosure provides for seamless steel formed using the high temperature TMCP process and the final (mandatory) heat treatment described hereinabove, with an interim austenitization treatment (mandatory) step therebetween.

As used herein, the term “interim austenitization treatment process,” and grammatical variants thereof, refers to a non-deforming steel heat treatment held at a temperature above Ac3 (i.e., the critical temperature at which free ferrite is completely transformed into austenite) for a period of time, followed by quenching. It is to be understood that while the present disclosure discusses the interim austenitization treatment process with reference to the formation of seamless steel, the interim austenitization treatment may equally be applied to form any type of linepipe without limitation.

Unlike traditional austenitization treatments, which are typically performed only several degrees above Ac3 (e.g., Ac3 to less than Ac3+50° C.) to minimize austenite growth in favor of finer microstructure after quenching, the interim austenitization treatments of the present disclosure employ higher temperatures to coarsen austenite grain size to promote lath bainite microstructure. In one or more aspects, steel formed after completion of a high temperature TMCP process (or other formed steel process) may be subsequently interim austenitization treatment processed (i.e., prior to the final heat treatment described herein) at a temperature in the range of about (Ac3+50° C.) (i.e., the Ac3 temperature plus 50° C.) to about (Ac3+200° C.), such as in the range of about (Ac3+50° C.) to about (Ac3+150° C.), or in the range of about (Ac3+75° C.) to about (Ac3+100° C.), encompassing any value and subset therebetween.

In one or more aspects, the heating rate for the interim austenitization treatment may be in the range of about 0.1° C. per second (° C./sec) to about 100° C./sec, encompassing any value and subset therebetween; such rates may depend on a number of factors including, but not limited to, the type of heating used (e.g., induction heating v. non-induction heating).

Upon reaching the desired temperature during the interim austenitization treatment, it is maintained stable for a predetermined length of time, such as in the range of greater than about one (1) minute to about 10 hours, encompassing any value and subset therebetween, such as about minutes to about 8 hours, or about 10 minutes to about 6 hours, or about 10 minutes to about 5 hours, or preferably about 10 minutes to about 3 hours, or about 10 minutes to about 2 hours, and thereafter followed by quenching. Quenching includes accelerated cooling, wherein a fluid is used to increase cooling rate (as opposed to air cooling); other quenching methods may also be employed, without departing from the scope of the present disclosure.

After the interim austenitization treatment, the carbon steel may be thereafter processed according to the final heat treatment process described hereinabove. When the formed carbon steel is a seamless pipe, the interim austenitization treatment and the final heat treatment process are both mandatory. When the formed carbon steel is a non-seamless pipe (e.g., a plate formed into a tubular linepipe, such as by welding), the interim austenitization treatment and the final heat treatment are both optional after the high temperature TMCP of the present disclosure, alone or in combination.

The present disclosure provides, among others, the following aspects, each of which may be considered as optionally including any alternate aspect.

Clause 1. A method comprising: heating a carbon steel composition to a first reheating temperature, the first reheating temperature being greater than about 1175° C.; deforming the composition while the composition is at a temperature in the range of the reheating temperature and a finishing temperature of greater than about Ar3; and quenching the composition into a formed carbon steel.

Clause 2. The method of Clause 1, wherein the first reheating temperature is in the range of about 1175° C. and about 1350° C.

Clause 3. The method of Clause 1 or Clause 2, further comprising maintaining stable the first reheating temperature for a length of time greater than about one minute.

Clause 4. The method of Clause 3, further comprising maintaining stable the first reheating temperature for a length of time in the range of greater than about one minute to about hours.

Clause 5. The method of any of the preceding clauses, wherein the deforming comprises at least one hot rolling step.

Clause 6. The method of Clause 5, wherein the deforming comprises at least two hot rolling steps having an extended interpass duration therebetween.

Clause 7. The method of Clause 6, wherein the extended interpass duration is in the range of about 10 seconds to about 10 minutes.

Clause 8. The method of Clause 6 or Clause 7, wherein the extended interpass duration is at a temperature of greater than about 950° C.

Clause 9. The method of any of the preceding Clauses, wherein the quenching comprises accelerated cooling.

Clause 10. The method of Clause 9, wherein the accelerated cooling comprises cooling the composition at a rate in the range of about 1° C. per second to about 300° C. per second.

Clause 11. The method of any of the preceding Clauses, further comprising ceasing quenching when the composition reaches a temperature of equal to or less than about 500° C.

Clause 12. The method of any of the preceding Clauses, wherein the carbon steel composition comprises one or more elements selected from the group consisting of manganese, carbon, phosphorous, sulfur, silicon, aluminum, chromium, molybdenum, niobium, titanium, nitrogen, calcium, nickel, vanadium, boron, and any combination thereof.

Clause 13. The method of any of the preceding Clauses, wherein after quenching, the formed carbon steel has a microstructure comprising lath bainite.

Clause 14. The method of Clause 13, wherein the formed carbon steel further comprises a microstructure having one or both of acicular ferrite and granular bainite.

Clause 15. The method of any of the preceding Clauses, wherein the formed carbon steel has a SSC arrest toughness (K_(ISSC)) of greater than about 20 ksi-in ° 5 or greater than about 35 ksi-in^(0.5).

Clause 16. The method of any preceding Clauses, further comprising forming the formed carbon steel into linepipe.

Clause 17. The method of any of the preceding Clauses, further comprising, after the quenching, reheating the formed carbon steel to a second reheating temperature.

Clause 18. The method of Clause 17, further comprising quenching the formed carbon steel after reheating the composition to the second reheating temperature, and thereafter, reheating the formed carbon steel to a third reheating temperature.

Clause 19. A formed carbon steel prepared according to a method comprising: heating a carbon steel composition to a first reheating temperature, the first reheating temperature being greater than about 1175° C.; deforming the composition while the composition is at a temperature in the range of the reheating temperature and a finishing temperature of greater than about Ar3; and quenching the composition.

Clause 20. The formed carbon steel of Clause 19, wherein the first reheating temperature is in the range of about 1175° C. and about 1350° C.

Clause 21. The formed carbon steel of Clause 19 or Clause 20, further comprising maintaining stable the first reheating temperature for a length of time greater than about one minute.

Clause 22. The formed carbon steel of Clause 19 to Clause 21, wherein the first reheating temperature is maintained for a length of time in the range of greater than about one minute to about 10 hours.

Clause 23. The formed carbon steel of Clause 19 to Clause 22, wherein the deforming comprises at least one hot rolling step.

Clause 24. The formed carbon steel of Clause 23, wherein the deforming comprises at least two hot rolling steps having an extended interpass duration therebetween.

Clause 25. The formed carbon steel of Clause 24, wherein the extended interpass duration is in the range of about 10 seconds to about 10 minutes.

Clause 26. The formed carbon steel of Clause 24 or Clause 25, wherein the extended interpass duration is at a temperature of greater than about 950° C.

Clause 27. The formed carbon steel of Clause 19 to Clause 26, wherein the quenching comprises accelerated cooling.

Clause 28. The formed carbon steel of Clause 27, wherein the accelerated cooling comprises cooling the composition at a rate in the range of about 1° C. per second to about 300° C. per second.

Clause 29. The formed carbon steel of Clause 19 to Clause 28, further comprising ceasing quenching when the composition reaches a temperature of equal to or less than about 500° C.

Clause 30. The formed carbon steel of Clause 19 to Clause 29, wherein the carbon steel composition comprises one or more elements selected from the group consisting of manganese, carbon, phosphorous, sulfur, silicon, aluminum, chromium, molybdenum, niobium, titanium, nitrogen, calcium, nickel, vanadium, boron, and any combination thereof.

Clause 31. The formed carbon steel of Clause 19 to Clause 30, wherein after quenching, the carbon steel plate has a microstructure comprising lath bainite.

Clause 32. The formed carbon steel of Clause 31, wherein the carbon steel plate further comprises a microstructure having one or both of acicular ferrite and granular bainite.

Clause 33. The formed carbon steel of Clause 19 to Clause 32, wherein the carbon steel plate has a SSC arrest toughness (K_(ISSC)) of greater than about 20 ksi-in ° 5 or greater than about 35 ksi-in^(0.5).

Clause 34. The formed carbon steel of Clause 19 to Clause 33, wherein the formed carbon steel is a carbon steel plate.

Clause 35. The formed carbon steel of Clause 19 to Clause 33, further comprising, after the quenching, reheating the composition to a second reheating temperature.

Clause 36. The formed carbon steel of Clause 35, wherein the second reheating temperature is in the range of about (Acl−300° C.) to about Acl.

Clause 37. The formed carbon steel of Clause 35, wherein the second reheating temperature is in the range of about (Acl−200° C.) to about Acl.

Clause 38. The formed carbon steel of Clause 35, wherein the second reheating temperature is in the range of about (Acl−100° C.) to about Acl.

Clause 39. The formed carbon steel of Clause 35 to Clause 38, further comprising maintaining stable the second reheating temperature for a length of time greater than about one minute.

Clause 40. The formed carbon steel of Clause 39, further comprising maintaining stable the second reheating temperature for a length of time in the range of greater than about one minute to about 10 hours.

Clause 41. The formed carbon steel of Clause 39, further comprising maintaining stable the second reheating temperature for a length of time in the range of greater than about 10 minutes to about 3 hours.

Clause 42. The formed carbon steel of Clause 35 to Clause 41, further comprising cooling the composition after the second reheating.

Claim 43. The formed carbon steel of Clause 42, wherein the formed carbon steel is a carbon steel plate.

Claim 44. The formed carbon steel of Clause 35 to Clause 42, further comprising, before the second reheating, interim austenitizing the composition at an interim austenitizing temperature and, thereafter, quenching the composition after the interim austenitizing.

Clause 45. The formed carbon steel of Clause 44, wherein the interim austenitizing temperature is in the range of (Ac3+50° C.) to about (Ac3+200° C.).

Clause 46. The formed carbon steel of Clause 44 or Clause 45, wherein the formed carbon steel is a carbon steel plate or a seamless pipe.

Clause 47. A method comprising: forming a formed carbon steel; and thereafter, reheating the formed carbon steel to a reheating temperature.

Clause 48. The method of Clause 47, further comprising preparing the formed carbon steel.

Clause 49. The method of Clause 48, wherein the preparing is by a thermo-mechanically controlled process.

Clause 50. The method of Clause 47 or Clause 49, wherein the reheating temperature is in the range of about (Acl−300° C.) to about Acl.

Clause 51. The method of Clause 50, wherein the reheating temperature is in the range of about (Acl−200° C.) to about Acl.

Clause 52. The method of Clause 51, wherein the reheating temperature is in the range of about (Acl−100° C.) to about Acl.

Clause 53. The method of Clause 47 to Clause 52, further comprising maintaining stable the reheating temperature for a length of time greater than about one minute.

Clause 54. The method of Clause 53, further comprising maintaining stable the reheating temperature for a length of time in the range of greater than about one minute to about hours.

Clause 55. The method of Clause 53, further comprising maintaining stable the reheating temperature for a length of time in the range of greater than about 10 minutes to about 3 hours.

Clause 56. The method of any of Clause 47 to Clause 55, further comprising, after the reheating, cooling the reheated formed carbon steel.

Clause 57. The method of any of Clause 47 to Clause 56, wherein the formed carbon steel is in a shape of a plate or a pipe.

To facilitate a better understanding of the aspects of the present disclosure, the following examples of preferred or representative are given. In no way should the following examples be read to limit, or to define, the scope of the present disclosure.

EXAMPLE Example 1— TMCP Materials with ˜YS 55-80 Ksi According to the Present Disclosure

In this example, various carbon steels were prepared according to one or more aspects of the high RHT/FRT TMCP methods of the present disclosure and tested for mechanical properties and SSC resistance, including the effect of subsequent final heat treatment.

Four (4) carbon steel samples (ID1-ID4) having the composition listed in Table 1, based on weight percent (wt. %), were evaluated in this example. Examples of constituents of the composition may include, among other elements, carbon (C), manganese (Mn), phosphorous (P), sulfur (S), silicon (Si), aluminum (Al), chromium (Cr), molybdenum (Mo), niobium (Nb), titanium (Ti), nitrogen (N), calcium (Ca), nickel (Ni), vanadium (V), boron (B), and any combination thereof.

TABLE 1 ID1 ID2 ID3 ID4 C 0.042 0.064 0.045 0.045 Mn 1.38 1.41 1.38 1.42 P 0.010 0.010 0.004 0.009 S 0.001 0.001 0.001 0.001 Si 0.245 0.261 0.240 0.245 Al 0.005 0.008 0.038 0.028 Cr 0.21 0.21 0.21 0.21 Mo 0.11 0.10 0.11 0.11 Nb 0.030 0.030 0.030 0.029 Ti 0.009 0.014 0.014 0.014 N 0.0039 0.0049 0.0034 0.0038 Ca 0.0011 0.0008 0.0013 0.0011

Carbon steels were prepared using the compositions of ID1-ID4 using vacuum induction melting (VIM), producing ingots of approximately 50 kg having a width of about 125 ‘millimeters (mm) and a thickness of about 125 mm. The ingots were each TMCP treated according to either a traditional TMCP method (represented by ID1 and ID2) or a TMCP method according to various aspects of the present disclosure (represented by ID3 and ID4). Generally, the ingots were reheated at a reheating temperature (RHT), and thereafter control hot rolled to a final thickness of about 20-25 mm at a particular finishing rolling temperature (FRT). Each of ID1-ID4 underwent between eleven (11) and thirteen (13) hot rolling passes to achieve the final thickness. The FRT was selected at a temperature greater than Ar3, the temperature at which austenite begins phase transformation onset during cooling (transformation to ferrite and/or bainite) and with various interpass durations, including at least one extended interpass duration, as defined hereinabove (temperature and time), followed by accelerated cooling control (ACC) at a cooling rate of greater than about 5° C./sec (e. g., in the range of about 5° C./sec to about 50° C./sec, or about 20° C./sec to about 50° C./sec) to ambient temperature. The specific TMCP parameters for this Example are provided in Table 2; actual extended interpass temperatures ranged between 950° C. to 1150° C. due to production conditions and equipment requirements.

TABLE 2 RHT (° C.) FRT (° C.) Extend Interpass ID1 1150 770 Yes ID2 1150 900 No ID3 1230 925 Yes ID4 1230 950 Yes

The TMCP treated ID1-ID4 carbon steels were evaluated for mechanical properties and SSC resistance. Mechanical properties, including yield strength (YS) measured in kip per square inch (ksi), tensile strength (TS) measured in ksi, and percent elongation (EL), were tested according to sub-size round bar with 1″ gauge length of ASTM-E8.

SSC resistance was evaluated using double cantilever beam (DCB) testing, using standard NACE TM0177 Method D (2016) test method, which is based on crack-arrest fracture mechanics (or decaying K loading) for high strength carbon steels. DCB testing measures the resistance of environmental cracking (EC) propagation (typically aligned with the rolling direction of steel plates or the longitudinal direction of tubular products), expressed in terms of a critical stress intensity factor (K_(ISSC)) measured in ksi-in^(0.5). DCB testing permits quantitative measurement of the SSC arrest toughness (K_(ISSC)); each K_(ISSC) reported herein is an average K_(ISSC) (of all observed cracks). DCB testing was performed by exposing samples of ID1-ID4 in the standard NACE A sour solution, representing a severe sour condition, for 14 days (336 hours). The standard NACE A sour solution comprises 5 wt. % sodium chloride and 0.5 wt. % acetic acid saturated with 100% hydrogen sulfide gas at 1 bar and an initial pH of 2.7. The standard NACE A sour solution belongs to the severe sour region (Region 3) in the NACE diagram of pH2S vs. pH per NACE MR-0175. The range of average K_(ISSC) with reference to the formed steel of the present disclosure is accordingly with reference to NACE MR-0175 with NACE A conditions at 1 bar, unless otherwise specified.

The mechanical and SSC resistance results of hot rolled materials are provided in Table 3.

TABLE 3 YS (ksi) TS (ksi) EL (%) K_(ISSC) (ksi-in^(0.5)) ID1 58.9 80.0 32.5 30.0 ID2 67.0 90.1 27.5 35.0 ID3 59.6 78.3 31.0 39.1 ID4 62.3 87.4 30.5 36.1

The results indicate that the samples produced under higher RHT/FRT TMCP conditions (ID3 and ID4) with extended interpass time exhibited greater SSC resistance (as represented by larger K_(ISSC) values) compared to those with traditional, relatively lower RHT/FRT TMPC conditions (ID1 and ID2). Moreover, the mechanical properties of the produced steels using the TMCP methods of the present disclosure are suitable for use as linepipe. Accordingly, in some aspects, the steel plates formed in accordance with the methods of the present disclosure may have a K_(ISSC) of greater than about 35 ksi-in^(0.5), such as in the range of about 35 ksi-in^(0.5) to about 60 ksi-in^(0.5), encompassing any value and subset therebetween.

To evaluate the effect of the final heat treatment step described in the present disclosure, heat (HT) was applied to each of ID1-ID4 and the metals were thereafter tested for mechanical properties and SSC resistance, as described above. ID1 was exposed to a final heat treatment at 575° C. and ID2-ID4 were exposed to a final heat treatment at 625° C., each for two (2) hours and allowed to cool to room temperature. The results are shown in Table 4.

TABLE 4 YS (ksi) TS (ksi) EL (%) K_(ISSC) (ksi-in^(0.5)) ID1 69.5 79.0 36.0 32.1 ID2 78.0 89.8 32.0 42.6 ID3 65.3 77.3 39.5 47.7 ID4 71.0 84.5 35.5 48.9

Compared to the results in Table 3 (without final heat treatment), each of ID1-ID4 exhibited enhanced SSC resistance after the final heat treatment, as shown in Table 4. ID1 improved by 7%; ID2 improved by about 22%; ID3 improved by about 22%; and ID4 improved by about 35%. Moreover, the final heat treatment step resulted in increased yield strength and, if at all, marginally decreased tensile strength while improving K_(ISSC).

Accordingly, in some aspects, the final heat treatment methods of the present disclosure may provide comparatively (e.g., to identical compositions without the final heat treatment) enhanced SSC resistance by greater than about 5%, including greater than about 7%, such as in the range of greater than about 5% to about 45%, or greater than about 5% to about 40%, encompassing any value and subset therebetween. Moreover, the final heat treatment reveals a synergistic effect when combined with the high temperature TMCP process of the present disclosure, including, if not an even more pronounced synergistic effect at higher temperatures within the ranges of the TMCP process of the present disclosure.

Example 2— Materials with ˜YS 80-120 Ksi after Heat Treatment According to the Present Disclosure

In this example, various carbon steels were prepared according to one or more aspects of the high RHT/FRT TMCP methods of the present disclosure and tested for mechanical properties and SSC resistance, including the effect of subsequent final heat treatment. This example covers higher strength grade of newly developed TMCP linepipe steels.

Three (3) carbon steel samples (ID5-ID7) having the composition listed in Table 5, based on weight percent (wt. %), were evaluated in this example. Examples of constituents of the composition may include, among other elements, carbon (C), manganese (Mn), phosphorous (P), sulfur (S), silicon (Si), aluminum (Al), chromium (Cr), molybdenum (Mo), niobium (Nb), nitrogen (N), nickel (Ni), boron (B), and any combination thereof. The symbol “—” indicates that the particular constituent was omitted.

TABLE 5 ID5 ID6 ID7 C 0.04 0.04 0.10 Mn 1.27 1.30 1.26 P 0.007 0.007 0.007 S <0.005 <0.005 <0.005 Si 0.380 0.370 0.410 Al 0.030 0.030 0.030 Cr 0.210 0.210 0.390 Mo 0.100 0.100 0.200 Ni — — 0.770 Nb 0.060 0.090 0.060 B 0.0005 0.001 — N 0.003 0.003 0.003

Three (3) ingots were prepared according to the methods described in Example 1, with additional details provided below. ID5 and ID6 are based on 0.04% carbon alloyed with Cr, Mo, Nb and B to achieve YS>80 ksi. The Nb content of ID5 and ID6 is 0.060% and 0.090%, respectively. ID7 increases carbon content to 0.10% with higher Cr, Mo and Ni amount compared to ID5 and ID7. Generally, the ingots were reheated to 1230° C., then hot rolled to a final thickness of 20 mm by TMCP methods (11 passes) according to various aspects of the present disclosures. The FRT of 950° C. was selected at a temperature greater than Ar3, the temperature at which austenite begins phase transformation onset during cooling (transformation to ferrite and/or bainite) including at least one extended interpass duration, as defined hereinabove (temperature and time), with actual extended interpass temperatures ranging between 950° C. to 1150° C. due to production conditions and equipment requirements. Accelerated cooling control (ACC) was at a cooling rate of greater than about 5° C./sec (e.g., in the range of about 5° C./sec to about 50° C./sec, or about 20° C./sec to about 50° C./sec) to ambient temperature. The processing parameters of TMCP method listed in Table 6. Heat treatment was applied on hot rolled materials. ID5-ID7 were heated to 625° C. and 675° C. for 3 hours, followed by cooling to room temperature.

TABLE 6 RHT (° C.) FRT (° C.) Extend Interpass ID5 1230 950 Yes ID6 1230 950 Yes ID7 1230 950 Yes

The heat treated ID5-ID7 carbon steels were evaluated for mechanical properties and SSC resistance as described in Example 1. The results are shown in Table 7. ID5-ID7 show higher strength, YS>80 ksi at the cost of SSC resistance compared with ID2-ID4 in Table 4. Higher heat treatment temperature (625° C. vs. 675° C.) improves SSC resistance with slight a decrease in YS. A higher fraction of lath bainite (ID5 vs. ID7) increases the strength without the decrease in SSC resistance.

TABLE 7 HT (° C.) YS (ksi) TS (ksi) EL (%) K_(ISSC) (ksi-in^(0.5)) ID5 625 95.8 106.0 26.0 30.2 ID5 675 82.0 101.5 25.5 31.9 ID6 625 100.0 110.5 27.5 28.4 ID6 675 97.5 107.0 27.0 31.4 ID7 625 112.5 125.5 24.0 27.1 ID7 675 110.5 112.5 25.5 32.4

FIGS. 3A-3F show the representative micrographs of heat treated ID5-ID7. FIGS. 3A, 3C, and 3E are micrographs of ID5-ID7 heat treated at 625° C., respectively. FIGS. 3B, 3D and 3F are micrographs of ID5-ID7 heat treated at 675° C., respectively. ID5-ID7 show the mixture of granular bainite and lath bainite. As increasing alloying content, the fraction of lath bainite increases from ID5 to ID7 along with newly disclosed TMCP processes. Accordingly, in some aspects, the steel plates formed in accordance with the methods of the present disclosure may have a K_(ISSC) of greater than about 20 ksi-in^(0.5), such as in the range of about 25 ksi-in^(0.5) to about 60 ksi-in^(0.5), encompassing any value and subset therebetween.

Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the present specification and associated claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the incarnations of the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claim, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

One or more illustrative incarnations incorporating one or more aspects and elements are presented herein. Not all features of a physical implementation are described or shown in this application for the sake of clarity. It is understood that in the development of a physical embodiment incorporating one or more elements of the present disclosure, numerous implementation-specific decisions must be made to achieve the developer's goals, such as compliance with system-related, business-related, government-related and other constraints, which vary by implementation and from time to time. While a developer's efforts might be time-consuming, such efforts would be, nevertheless, a routine undertaking for those of ordinary skill in the art and having benefit of this disclosure.

While compositions and methods are described herein in terms of “comprising” various components or steps, the compositions and methods can also “consist essentially of” or “consist of” the various components and steps.

Therefore, the various aspects of the present disclosure are well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular examples and configurations disclosed above are illustrative only, as the present disclosure may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative examples disclosed above may be altered, combined, or modified and all such variations are considered within the scope and spirit of the present disclosure. The aspects illustratively disclosed herein suitably may be practiced in the absence of any element that is not specifically disclosed herein and/or any optional element disclosed herein. While compositions and methods are described in terms of “comprising,” “containing,” or “including” various components or steps, the compositions and methods can also “consist essentially of” or “consist of” the various components and steps. All numbers and ranges disclosed above may vary by some amount. Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles “a” or “an,” as used in the claims, are defined herein to mean one or more than one of the element that it introduce 

1. A method comprising: heating a carbon steel composition to a first reheating temperature, the first reheating temperature being greater than about 1175° C.; deforming the composition while the composition is at a temperature in the range of the reheating temperature and a finishing temperature of greater than about Ar3; and quenching the composition into a formed carbon steel.
 2. The method of claim 1, further comprising maintaining stable the first reheating temperature for a length of time greater than about one minute.
 3. The method of claim 1, wherein the deforming comprises at least one hot rolling step.
 4. The method of claim 3, wherein the deforming comprises at least two hot rolling steps having an extended interpass duration therebetween.
 5. The method of claim 1, wherein the quenching comprises accelerated cooling.
 6. The method of claim 1, wherein after quenching, the formed carbon steel has a microstructure comprising lath bainite.
 7. The method of claim 1, wherein the formed carbon steel has a SSC arrest toughness (K_(ISSC)) of greater than about 35 ksi-in^(0.5).
 8. The method of claim 1, wherein the formed carbon steel has a SSC arrest toughness (K_(ISSC)) of greater than about 20 ksi-in^(0.5).
 9. The method of claim 1, further comprising, after the quenching, reheating the formed carbon steel to a second reheating temperature.
 10. The method of claim 9, further comprising quenching the formed carbon steel after reheating the composition to the second reheating temperature, and thereafter, reheating the formed carbon steel to a third reheating temperature.
 11. A formed carbon steel prepared according to a method comprising: heating a carbon steel composition to a first reheating temperature, the first reheating temperature being greater than about 1175° C.; deforming the composition while the composition is at a temperature in the range of the reheating temperature and a finishing temperature of greater than about Ar3; and quenching the composition.
 12. The formed carbon steel of claim 11, further comprising maintaining stable the first reheating temperature for a length of time greater than about one minute.
 13. The formed carbon steel of claim 11, wherein the deforming comprises at least one hot rolling step.
 14. The formed carbon steel of claim 13, wherein the deforming comprises at least two hot rolling steps having an extended interpass duration therebetween.
 15. The formed carbon steel of claim 11, wherein the quenching comprises accelerated cooling.
 16. The formed carbon steel of claim 11, wherein after quenching, the formed carbon steel has a microstructure comprising lath bainite.
 17. The formed carbon steel of claim 11, wherein the formed carbon steel has a SSC arrest toughness (K_(ISSC)) of greater than about 35 ksi-in^(0.5).
 18. The formed carbon of claim 11, wherein the formed carbon steel has a SSC arrest toughness (K_(ISSC)) of greater than about 20 ksi-in^(0.5).
 19. The formed carbon steel of claim 11, further comprising, after the quenching, reheating the composition to a second reheating temperature.
 20. The formed carbon steel of claim 19, wherein the second reheating temperature is in the range of about (Acl−300° C.) to about Ad.
 21. The formed carbon steel of claim 19, further comprising maintaining stable the second reheating temperature for a length of time greater than about one minute.
 22. The formed carbon steel of claim 19, further comprising, before the second reheating, interim austenitizing the composition at an interim austenitizing temperature and, thereafter, quenching the composition after the interim austenitizing.
 23. The formed carbon steel of claim 22, wherein the interim austenitizing temperature is in the range of (Ac3+50° C.) to about (Ac3+200° C.).
 24. A method comprising: forming a formed carbon steel; and thereafter, reheating the formed carbon steel to a reheating temperature.
 25. The method of claim 24, wherein the preparing is by a thermo-mechanically controlled process wherein the reheating temperature is in the range of about (Acl−300° C.) to about Acl.
 26. (canceled) 